This three-month study is designed to obtain data on the efficacy, safety and tolerability of Sinemet CR 25/100 in patients with stage I-II Parkinson's disease who had never received levodopa therapy. The pharmacokinetics of plasma levodopa will also be studied to determine if levodopa will progressively accumulate because of the sustained release formulation of Sinemet CR. The pharmacokinetics of single oral doses of two different strengths of Sinemet CR will also be studied.